environmental samples

A few Euryarchaeotes thrive in thermal environments and some are extremely thermophilic; those with growth temperature optima over 80°C are called hyperthermophiles.
One of these organisms, Methanopyrus, is a methanogen and closely resembles the methanogens (Methanobacteria and Methanococci) in its basic physiology but is unusual in its extreme requirement for heat and phylogenetic position, distinct from that of other methanogens.